Abstract

Volutes are widely distributed in the Cenozoic record of Patagonia and Tierra del Fuego, where they are represented by the South American endemic genera AdelomelonDall, 1906, PachycymbiolaIhering, 1907, OdontocymbiolaClench and Turner, 1964, and MiomelonDall, 1907. These taxa have been restricted to the southwestern Atlantic and southeastern Pacific Oceans from Tertiary times to the Recent, and since their earliest record in the ?Middle Eocene–Late Oligocene–earliest Miocene they have evolved adaptations to variations in water depth and temperature. These ecological adaptations were less marked for Adelomelon and Pachycymbiola, which have achieved a similar geographical pattern since the Tertiary, but they were strongly modified in Miomelon. In the Atlantic, Miomelon migrated southwards from the shallow and warm-temperate waters that it typically inhabited during the Tertiary, to deeper, colder waters of the Recent Magellanic Province and Subantarctic region, where it is restricted at present. A detailed discussion of the validity of Tertiary genus ProscaphellaIhering, 1907 herein concludes it to be a synonym of MiomelonDall, 1907. Seven species are redescribed and illustrated: Adelomelon pilsbryi (Ihering), A. cannada (Ihering), A. (Pachycymbiola) ameghinoi Ihering, ?Pachycymbiola feruglioi (Doello Jurado), Miomelon gracilior (Ihering), M. dorbignyana (Philippi), and M. petersoni (Ortmann); and four new ones are described: Miomelon castilloensis, Pachycymbiola chenquensis, P. camachoi, and P. arriolensis.

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